Freeze-resistant metering valve

ABSTRACT

The invention relates to a freeze-resistant metering valve that comprises a magnetic part and a hydraulic part. The magnetic part has an armature biased by a spring. The hydraulic part has an annular space for receiving and conveying a liquid as well as a tappet facing a valve seat. The valve seat comprises a nozzle opening on the side facing away from the tappet. In a currentless state, the tappet blocks the annular space in the direction of an opening (nozzle opening) until the freezing pressure onto the armature generates a sufficient force by virtue of the solidifying liquid. This force is used to counteract the spring force until a freeze expansion space is created by way of a relieving motion.

This application is a continuation of International Application No.PCT/EP2005/052226 filed on May 13^(th), 2005, which application claimspriority of German Patent Application No. 10 2004 025 062.6 filed on May18^(th), 2004.

BACKGROUND OF THE INVENTION

The invention relates to a freeze-resistant metering valve which can beused in automotive engineering, in particular utility vehicles. Thefreeze-resistant metering valve is, in particular, suitable for exhaustgas after treatment systems and/or exhaust systems.

Motor vehicles, in particular utility vehicles which are intended to beused in regions with a temperate climate or even arctic regions, have tobe designed so that they can even withstand temperatures below zerodegrees Celsius without sustaining damage. This is generally possible bythe choice of suitable materials. Alternatively, for many years anadditional source of heat has been used when temperatures fall too low.

In order to reduce Nitrogen Oxide (NOx) in the exhaust gas of motorvehicles, in particular diesel vehicles, automobile manufacturers andsuppliers have agreed to use a 32.5% urea-water solution (UWS). Due tothe high proportion of water in the solution, even at low negativetemperatures (degrees Celsius), the solution which is pressurized duringoperation freezes.

For many years now, the industry has been concerned with how thefreezing of the urea-water solution can be tackled. One solutionconsists in removing all the UWS by means of compressed air whenswitching off the motor vehicle. The system only functions when an aircompressor is present on board the vehicle. An air pressure generator isincorporated in large utility vehicles as standard. No specific airsupply system is provided in small utility vehicles and automobileswhich are equipped with a diesel engine.

The costly algorithms with which a control device is to be programmed,so that faulty behavior due to freezing can be identified, can be seenfrom DE 10256169 A (Toyota Motor Corporation Ltd).

DE 10139139 A (Robert Bosch GmbH) proposes to provide the reducing agentline with electrical heating in order to eliminate freezing of thereducing agent. The fact that this is impractical can be seen from DE19935920 A (Siemens AG). It can be seen here that the heating powerrequirement for the reducing agent reservoir alone would exceed onekilowatt. Therefore, it can be further seen from the publication that aheat exchanger can be incorporated. According to DE 10139142 A (RobertBosch GmbH) the heat exchanger has to prevent freezing, even attemperatures below −11° C. The requirements of automobile manufacturersgo even further. They require the valves to work perfectly even at anoutside temperature of −40° C. It has been considered, therefore, as inDE 4432577 A (Siemens AG), to incorporate a special back-flow preventionvalve with variable control operation. DE 4432576 A (Siemens AG) alsorefers to the difficulty of using frost protection agents. Operatingwith different volumes is therefore possible.

What all these solutions have in common is that additional measures haveto be taken to tackle the risk of freezing. It would be desirable tohave a freeze-resistant metering valve which operates perfectly at thehigh temperatures of the exhaust gas stream which can exceed 700° C. andis simultaneously freeze-resistant. Even at an outside temperature of−40° C., the metering valve still has to be able to be operated,provided that the UWS is present in liquid form. Therefore, the entiresystem in which the metering valve is incorporated is to be of energyefficient design.

SUMMARY OF THE INVENTION

These and other advantages are fulfilled by a freeze-resistant meteringvalve according to the invention and a corresponding exhaust gascleaning system. Various advantageous embodiments are disclosed herein.

The freeze-resistant metering valve is intended to be electricallycontrollable. As a result, the vehicle controller or a control deviceparticularly appropriate for the exhaust gas stream can meter thecorrect amount of UWS. The invention can also be used for other liquidswhich are to be metered. Aspects of the invention are also thereforeexplained for other liquids. In normal operation, when the entireexhaust gas stream, including exhaust pipes and mufflers, is heated bythe waste heat of the engine, no particular attention has to be paid tothe risk of freezing. It is dangerous when the vehicle is no longer, ornot, in operation. In every state under particular consideration, nocontrol signal, i.e. no current, is passed through the valve. The tappetin the metering valve closes the opening through which the UWS is to beconveyed. When the temperature is lowered, for example, from 700° C. totemperatures below the freezing point of the UWS (approximately −11° C.)the metering valve would be permanently damaged, due to the expansion ofthe UWS, which can be approximately 9 to 11%. The freezing forces can beadvantageously used in a passive system, by being converted into arelieving motion. The relieving motion produces a freeze expansionspace. One possibility is that the relieving motion acts in a controlledmanner. The relieving motion acts indirectly or directly on the armaturein order to produce a freeze expansion space by a movement of thetappet. A freeze expansion space has to be established within the valve.This can be located at different positions. In one embodiment,therefore, the freeze expansion space is the region which is produced bylifting the tappet from the valve seat. However, a specific annularspace region can also be provided or a space which is only accessible tothe liquid by means of the relieving motion. When the pressure in one ofthe freeze expansion spaces is great enough, the resulting force exceedsthe opposing spring force. As a result, the armature can be displacedagainst the spring force and the tappet is lifted from the seat.

The invention is further characterized in that the amount of liquidwhich is present in the metering valve is reduced to a minimum. By aclever design of the valve, the space receiving the liquid is minimized,the tappet filling a portion of the space which is designed forconveying the liquid further into the exhaust gas stream, the annularspace. Moreover, unnecessary hollow spaces are filled by filling pieces,sleeves, bearings and other closure members. The minimizing of theannular space should be taken even further from the point of view offreeze resistance. However, the minimizing should not impede the flow ofthe material to be metered, the liquid. In other words, the pressureloss should not be noticeable. The pressure loss would be noticeable ata pressure loss of more than 5% of the nominal pressure of the meteringvalve. Preferably the pressure loss should even be under 1% of thenominal pressure of the metering valve. For example, it can be shownthat at a nominal pressure of 5 bar absolute, the pressure loss alongthe entire annular channel should not be over 250 mbar, preferably evenunder 50 mbar.

In a further advantageous embodiment, moreover, the metering valveoffers flexible expansion surfaces. Such expansion surfaces can beresilient bases or diaphragms. Due to the freezing pressure, a freezeexpansion space bulges out in the region of the resilient base or thediaphragm. If the liquid melts, such as for example the UWS, theresilient base or the diaphragm returns again to its original position.The original position is the operating position.

Moreover, according to a further advantageous aspect, in someembodiments of a freeze-resistant metering valve deliberate undercutsare avoided. Undercuts are avoided in the valves as, in the regions ofthe undercut, forces can be produced in all directions by the freezingpressure which can lead to damage. The spring which holds the tappet inthe currentless state in the locked position is supported such that, inits supported region, no undercuts are necessary. By avoiding undercuts,the freezing liquid is not obstructed.

Additional expansion spaces can be produced, for example, by the nozzleplate, which is present for the equal distribution of the liquid to bemetered and is capable of expansion, being able to be lifted from thenozzle opening.

The spring can optionally be located in the liquid.

By means of special seals and special rings, regions in the meteringvalves are sealed relative to the liquid and thus the amount of liquidpresent in the valve is reduced.

According to a further advantageous aspect, the metering valve can bedesigned such that the supply line discharges into a sleeve via anexpandable hose. The sleeve exterior thereof can be ribbed. Theexpandable hose can be slipped over the sleeve exterior. By means of theribbing of the sleeve exterior, the surroundings are sealed against theUWS. If the UWS freezes in the supply line or in the sleeve, theexpandable hose offers an additional compensation space. On the onehand, the hose itself can expand. On the other hand, it can easily belifted away from several ribs of the sleeve exterior and yet besealingly held by the remaining ribs of the sleeve exterior.

A further outlet can be provided for the valves. The outlet undertakestwo tasks. As, during operation, the metering valve has to be heatresistant and the UWS should not overheat on the inside (a desiredtemperature of less than 90° C. has to be maintained) it can benecessary during overheating that the nozzle neck of the hydraulic partis cooled by additional liquid. To this end, during the constantcirculation of the UWS, said UWS is cooled by the hydraulic part. In thecase of freezing of the liquid, the additional outlet undertakes thetask of switching the valve to the unpressurized state and also offersan additional expansion space.

By pressing the tappet with stop plates, sleeve armatures or annulararmatures, a large surface is provided for the freezing pressure. Thelarge surface converts the force of the freezing pressure of the minimalliquid present into a large force which can act against the spring.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding, reference is made to the following Figures,whereby

FIG. 1 discloses a first embodiment,

FIG. 2 discloses a second embodiment,

FIG. 3 discloses a third embodiment, and

FIG. 4 illustrates a section through a nozzle neck of an embodimentaccording to FIG. 1 or 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the Figures, similar components are numbered with the same referencenumerals, even when there are small structural differences.

FIG. 1 discloses a metering valve 1. The metering valve 1 comprises ahydraulic part 3 and a magnetic part 5. The magnetic part 5 has a coil7, which has numerous windings and is arranged on a coil support 9. Onthe corners of the coil support are provided seals 49 which can be, forexample, O-rings. The seals 49 seal the coil support relative to themagnet housing 11 around the pole core 61. The metering valve is, as awhole, rotationally symmetrically constructed. A bore is provided in itscenter. The tappet 17 moves in the bore. The space which remains of thebore is an annular space 19. The tappet is partially surrounded by anarmature which is a sleeve armature 13′. The tappet 17 which leads intothe valve seat 21 at its one end, is rounded at the end. On the otherend, the tappet 17 leads into an armature sleeve 51. The valve seat 21is a part of the end piece 23 which also surrounds the nozzle opening25. Optionally, a nozzle plate 27 can be arranged on the end piece 23.The nozzle plate 27 attenuates the droplets of liquid which are alreadyatomized by the funnel-shaped nozzle opening 25 and by the nozzle 73.The UWS is introduced without compressed air into the exhaust gasstream. It can therefore be necessary for the liquid to be atomizedfurther. A bearing 57 is provided in the vicinity of the end piece 23 bymeans of which the liquid space is minimized. The bearing 57 guides thetappet 17. The liquid space is further minimized by the sleeve 59.Compensation spaces are intentionally provided on the other side. Theopening 45, for example, which is a second opening, serves to relievethe pressure and in the frozen state serves as an outlet to acompensation space, for example in an expansion hose which can beoptionally present. The ring 47 undertakes a plurality of tasks: itcirculates the magnetic flow, by interrupting the direct flow and sealsthe supply line and/or the annular space 19 relative to the coilsupport. Undercuts are avoided by means of the projections 43, on whichthe spring 15 can be supported. The projections 43 are of such a sizethat the spring 15 is supported in a stable manner but no effect isproduced on the liquid in the supply line 35. On the other side of thespring 15, the spring presses against the armature 13 which is a sleevearmature 13′. Threaded projections are provided on the nozzle neck 67.By means of its nozzle exterior 39 which has a Christmas tree profile,the sleeve 37 is not only provided for the receipt of a resilient hose,but is also simultaneously the pole core 61 for the magnetic end of thecoil 7 on the armature 13′. In the currentless state, i.e. the state inwhich no current flows through the coil 7, the spring 15 presses thearmature 13′ via the tappet 17 against the valve seat 21. The biasing ofthe spring 15 is permanently present, provided that the spring is notrestricted in its expansion by freezing of the liquid in the supply line35. The tappet 17 is pressed via the sleeve 51 in the currentless stateby the spring force of the spring 15 against the valve seat 21 of theend piece 23. The annular space which, in this embodiment, is 5/10 mm(i.e., 0.5 mm) in total, receives only a minimal amount of liquid. Ifthis minimal amount of liquid freezes, the liquid is pressed against thedeformable diaphragm 33 and/or base 33′. The liquid can also be pressedinto the resilient hose. If the force exceeds that which is formed bythe internal pressure produced on the corresponding surface, the tappet17 is displaced against the spring force and the tappet 17 is liftedfrom the valve seat 21. As a result, compensation spaces are opened up.A first compensation space 29 and a second compensation space 31 areprovided in this embodiment. Moreover, the opening 45 is provided. Thefreezing liquid can be diverted into the compensation spaces 29 and 31which are located in the supply line 35 and the valve seat 21. Themagnet housing 11 is flanged at its ends and therefore presses the polecore 61 and the hydraulic part 3 against the ring 47. The magneticdiverter which the ring 47 represents, seals the two parts of the valveand is optionally welded. The shape of the valve housing 69 correspondsto the receiving unit, for example the exhaust of the motor vehicle, bymeans of recesses and projections depending on the contour.

In contrast to the metering valve 1 according to FIG. 1 which isprovided with an axial supply connector for the supply line 35, themetering valve 1 according to FIG. 2 is equipped with a lateralconnector. The two valves have a long metering valve neck, the nozzleneck 67, to ensure at a corresponding temperature gradient that, in therear portion of the valve, materials which are not so heat resistant areused for the spring 15 and the coil 7 as well as the supply line 35. Themetering valve 1 also has a hydraulic part 3 and a magnetic part 5. Thespring 15 is supported on the one hand against the magnet housing 11 andon the other hand relative to the armature 13, which is a flat armature.A coil 7 is located in the magnet housing 11. The tappet 17 which leadsinto the valve seat 21 via its rounded tip, has a shrink-fitted sleeve51 on its other end. The valve seat 21 in the end piece 23 leads intothe nozzle opening 25 which is covered by an optional nozzle plate 27for distributing the liquid. The metering valve 1 comprises twocompensation spaces 29 and 31 and has a further optional outlet 45. Thefirst space 29 is delimited by a diaphragm 33. The space 29 adopts thefunction of an compensation space by means of the diaphragm 33. On theside opposing the compensation space 29, a hollow space 55 is provided.The diaphragm 33 is connected by spot welds or by thick welds to thevalve housing 69 and the tappet 17. The diaphragm is made of metal. Theliquid is transferred to the metering valve from a resilient hose viathe supply line 35 in the sleeve 37 which has the sleeve side 39. In aless advantageous embodiment, a metal pipe can be provided instead of aresilient hose. As a result, however, a further compensation space islost. The liquid, which is present in the supply line 35, flows via theannular space 19 along the tappet 17 to the valve seat 21. When currentis applied to the coil 7, the armature 13 is pulled onto the coil 7. Inthe open state of the metering valve 1, the hollow space 55 is reducedor disappears. The spring 15 is pressed together by the armature 13. Atthe end of the operation of the motor vehicle, the coil 7 is switched tothe currentless state. The tappet 17 is lowered onto its valve seat 21.The liquid which is present in the compensation space 31 is dispensedvia the nozzle plate 27 into the exhaust gas stream of the vehicle. Ifthe liquid in the annular space 19 is frozen by corresponding cooling ofthe metering valve 1, the freezing liquid presses against the diaphragm33. The force of the freezing pressure is transferred via the disc 71 tothe armature 13. The armature 13 presses against the spring 15. Thetappet 17 is lifted from the valve seat 21 via the sleeve 51. Thecompensation space 31 is therefore opened up. The further compensationspace 29 which may be enlarged by the diaphragm 33, offers additionalspace for the expansion of the frozen liquid. Moreover, the opening 45which, however, does not have to be present, provides a compensationspace. The hydraulic part 3 is narrower than the magnetic portion 5. Asthe hydraulic portion 3 has to be produced from heat resistant material,it would be preferable to use as little as possible of the valuablematerial. The bearing 57 delimits the possible amount of liquid whichcan be present in the annular space 19. The bearing guides the needleand/or the tappet which is optionally provided with holes.

In FIG. 3 a further embodiment of a metering valve 1 according to theinvention is disclosed. The entire metering valve 1 consisting of ahydraulic part 3 and a magnetic part 5 is, for example, shorter than themetering valves according to FIGS. 2 and 1. It is, however, wider. Thegeometry of the valve part is adapted to requirements. The meteringvalve is also rotationally symmetrically constructed, with a fewexceptions. The armature 13″ is a tappet armature which leads into atappet 17 and has an armature bore 53. The spring 15, which is supportedrelative to the seal pot 63, engages on one side of the tappet armature13″. The seal pot 63 is equipped with a hollow space 55 which isintended to provide an expansion space for the volume from the space 29.The supply line 35 runs laterally to the tappet 17 which is partiallysurrounded by the inner space 19. The tappet 17 leads into the valveseat 21 of the end piece 23. The end piece 23, in this embodiment, isnot equipped with a nozzle plate. Also, the compensation space 31 in theregion of the nozzle opening 25 is smaller than in the metering valvesaccording to FIG. 1 or 2. The bearing 57 delimits the maximum amount ofliquid which can be located in the annular space 19 and in the supplyline 35. If current is applied to the coil 7, the armature 13 is movedby the magnetic field against the spring force of the spring 15 in thedirection of the pole core 61. As a result, the tappet 17 is lifted fromthe valve seat 21. In the currentless state, the tappet 17 sinks ontothe valve seat 21. If the fluid freezes in the supply line 35 or theannular space 19, the freezing liquid presses against the tappetarmature 13″, the tappet armature 13″ is moved against the spring 15. Asa result, the UWS in the space 29 is forced in the direction of theresilient base 33. The spring 15 is pressed together. The tappet 17 islifted from the valve seat 21. The liquid can be diverted into thecompensation space 31. When the compensation space is not sufficient, anadditional compensation space can be created by the resilient base 33 inthe region of the spring 15. The magnet housing 11 is simultaneously thevalve housing. The hollow space which is also a first compensation space29, is in fluidic connection with the supply line 35 and the annularspace 19 via the armature bore 53. The armature 13″ is supported orsurrounded on both sides by the liquid.

In FIG. 4 a further alternative possibility is shown of how the amountof liquid present can be further reduced. Instead of having a completelycircumferential annular space 19 along the entire tappet 17, the tappet17 is only partially provided with grooves and projections 65 a, 65 b,65 c and 65 d. The remaining volume of the nozzle neck 67 is made fromsolid material. Only the minimal liquid present in the eccentricopenings 65 a, 65 b, 65 c and 65 d can then still freeze. The solidmaterial of the nozzle neck 67 further contributes to the strength ofthe nozzle neck 67. A nozzle neck shown can be present in the valvesaccording to FIG. 1, FIG. 2 and also FIG. 3. The nozzle neck only has tobe correspondingly adapted in each case.

The valves according to the invention are preferably connected to aresilient hose through which the liquid is conveyed to the meteringvalve. The valve seat opens into the exhaust gas stream of the motorvehicle. With vehicles driven by diesel engines, a 32.5% urea-watersolution is conveyed through the valve. The freeze-resistant valves are,however, developed advantageously such that other liquids can also beconveyed through the metering valves. Thus pure water or salt water oreven diesel can be conveyed just as efficiently through the valves.

The valve is characterized in that, on the one hand, it can operate inan environment which may reach more than 700° C. and, on the other hand,even at temperatures as low as −40° C. it undergoes no permanent damage.To this end, it contributes to minimizing the amount of liquid insidethe valve. Moreover, only selected components are wetted by the liquid.The entire system operates passively in the frozen state. The systemitself is relieved during freezing. No additional sources of energy arerequired. The liquid wettable spaces and liquid containing spaces aredesigned without undercuts or interfering contours. Even when valveshave only one or other of the previously summarized features, they fallwithin the protective scope of this invention.

LIST OF REFERENCE NUMERALS

TABLE 1  1 Metering valve  3 Hydraulic part  5 magnetic part  7 coil(with windings)  9 coil support 11 magnet housing 13 armature as flatarmature 13′ armature as sleeve armature 13″ armature as tappet armature15 spring (helical compression spring) 17 tappet 19 annular space 21valve seat 23 end piece 25 nozzle opening 27 nozzle plate (optional) 29first compensation space (as part of the freeze expansion space) 31second compensation space (as part of the freeze expansion space) 33diaphragm 33′ resilient base 35 supply line 37 sleeve (ribbed exterior)39 sleeve exterior 41 spot welds 43 projections 45 opening (second) 47ring 49 O-ring seal 51 armature sleeve 53 armature bore 55 hollow space57 bearing 59 sleeve 61 pole core 63 seal pot 65 annular space openings(65a, 65b, 65c, 65d) 67 nozzle neck 69 valve housing 71 disc 73 nozzle

1. A freeze-resistant metering valve, comprising: a magnetic part and ahydraulic part, the magnetic part having an armature biased by a springand the hydraulic part having an annular space for receiving andconveying a liquid as well as a tappet facing a valve seat, and thevalve seat having a nozzle opening on a side facing away from thetappet, wherein in a currentless state, the tappet blocks the annularspace in the direction of said nozzle opening until a freeze expansionspace is created by means of a freezing pressure of a solidifying liquidonto the armature by way of a relieving motion.
 2. A freeze-resistantmetering valve as claimed in claim 1, wherein the relieving motion liftsthe tappet from the valve seat.
 3. A freeze-resistant metering valve asclaimed in claim 1, wherein the annular space extends along a specificportion of the tappet.
 4. A freeze-resistant metering valve as claimedin claim 1, wherein the length of the annular space is created such thatthe magnetic part is positioned in a markedly lower temperature rangethan the end piece of the hydraulic part of the valve.
 5. Afreeze-resistant metering valve as claimed in claim 1, wherein theliquid is preferably a urea-water solution.
 6. A freeze-resistantmetering valve as claimed in claim 1, wherein the diameter of theannular space is reduced to a minimum volume, without a noticeablepressure loss occurring along the annular space.
 7. A freeze-resistantmetering valve as claimed in claim 1, wherein the diameter of the tappetis smaller than, or equal to, 2 mm and the annular space 5/10 mm largerthan the tappet.
 8. A freeze-resistant metering valve as claimed inclaim 1, wherein the metering valve has a diaphragm or a resilient basein its interior.
 9. A freeze-resistant metering valve as claimed inclaim 8, wherein the diaphragm or the resilient base is present on theside of the tappet facing away from the valve seat.
 10. Afreeze-resistant metering valve as claimed in claim 8, wherein thediaphragm or the resilient base is in sealing contact with the valvehousing.
 11. A freeze-resistant metering valve as claimed in claim 1,wherein the spring is located in the liquid during operation.
 12. Afreeze-resistant metering valve as claimed in claim 1, wherein acompensation connection is provided in the armature.
 13. Afreeze-resistant metering valve as claimed in claim 12, wherein thepressure on two opposing sides of the armature is compensated by acompensation bore in the armature.
 14. A freeze-resistant metering valveas claimed in claim 1, wherein the hydraulic part of the metering valvehas a smaller diameter than the magnetic part of the metering valve. 15.A freeze-resistant metering valve as claimed in claim 1, wherein a discor a bearing is arranged in the vicinity of the valve seat.
 16. Afreeze-resistant metering valve as claimed in claim 15, wherein the discor the bearing is provided with eccentrically arranged through-passages.17. A freeze-resistant metering valve as claimed in claim 1, wherein thevalve is equipped with an axial connector for the liquid.
 18. Afreeze-resistant metering valve as claimed in claim 1, wherein thearmature has a round form and/or the armature has the form of a flatdisc.
 19. A freeze-resistant metering valve as claimed in claim 1,wherein a seal pot surrounds the armature as a friction bearing support.20. A freeze-resistant metering valve as claimed in claim 1, wherein asealing ring, which is preferably not magnetic, is provided to deflectthe magnetic flux in the region of the armature.
 21. A freeze-resistantmetering valve as claimed in claim 1, wherein an optional second outletcan be provided as an opening in the vicinity of the nozzle opening. 22.A freeze-resistant metering valve as claimed in claim 1, wherein thevalve seat can be optionally covered by a nozzle plate.
 23. Afreeze-resistant metering valve as claimed in claim 11, wherein thespring is fixedly held by at least two projections, preferably fourprojections, as stop faces and as a result forms no undercut which canhinder the flow of the freezing liquid.
 24. An exhaust gas cleaningsystem with a metering valve as claimed in claim 1, on whose liquidinlet a flexible hose is placed, and which is in fluidic communicationwith a motor vehicle exhaust gas system.
 25. A freeze-resistant meteringvalve, comprising: a magnetic part and a hydraulic part, the magneticpart having an armature biased by a spring, the hydraulic part having anannular space for receiving and conveying a liquid and a tappet facing avalve seat, and the valve seat having a nozzle opening, wherein themetering valve is itself passively relieved during freezing.